This invention relates to a lift jack control system and more particularly to a servo control for regulating the operation of a fork lift jack.
In manually controlled or semi-automatically controlled forklift operations the forklift raises the fork, usually by means of a hydraulic jack, to some desired height at which point the forklift jack is stopped. Because the fork may be carrying heavy loads it is necessary to slow the rate of ascent or descent of the fork shortly before the desired stopping point. If this is not done the fork may come to an abrupt halt which can upset the load or damage the forklift due to the inertia of the load and the fork.
In some prior control systems this is accomplished by automatically slowing the fork to some predetermined constant speed approximately one foot before the desired stopping point. This can produce lengthy delays in the final fork positioning and can greatly reduce the efficiency of any automatic or semi-automatic order picking system using such a forklift.
Still another disadvantage of some prior art forklift positioning control systems is that the raising and lowering of the forklift is operated automatically without being initiated by the operator. In some circumstances this can pose a danger to the operator and to bystanders due to unexpected movement and is a special problem because such systems can also get out of control.